1. Field of the Invention
This invention relates to an image processor for image-capturing an image sequence of a high frame rate at a high-sensitivity and a high-speed and to a method thereof.
2. Description of the Related Art
When the images are shot at a high-frame rate, the exposure time becomes so short that a dynamic range of a sufficient level is not obtained by using an ordinary image processor and the SN ratio decreases, too.
To shoot the images maintaining a high sensitivity, there can be chiefly contrived four methods.    1. To lengthen the exposure time.    2. To use bright lenses with a small F number.    3. To improve the sensitivity by contriving the circuit of the photo detector (PD).    4. To increase the exposure area by increasing the areas of the pixels.
Despite the above four methods are employed, however, there still remain the following problems.
With the first method, it is not allowed to lengthen the exposure time when it is attempted to shoot the images at a high-frame rate.
With the second method, the sensitivity can be improved by selecting a lens having a large diameter and a small F-number accompanied, however, by limitation.
With the third method, the sensitivity can be improved by contriving the circuit of the photo detector (PD) as taught in, for example, Japanese Patent Publication (kokai) 5-336314, however, by limitation.
With the fourth method, the sensitivity is improved by increasing the areas of the pixels and by increasing the exposure areas. It is, however, difficult to decrease noise due to dark current.
Japanese Patent Publication (Kokai) 2002-64750 proposes a method of improving sensitivity by adding signals of the neighboring pixels.
However, addition of the signals does not make it possible to obtain images maintaining high SN ratios though it may guarantee a dynamic range.